The invention relates to apparatus for monitoring a chemical mechanical polishing (CMP) process. More specifically, the invention relates to detection of anomalies associated with the CMP process. Additionally, the invention relates to a CMP pad and/or platen that is configured to allow such monitoring.
A wafer surface undergoing chemical mechanical polishing (CMP) is typically polished by rubbing the wafer, which is attached to a wafer carrier, against a pad that is atop a platen. A slurry is typically used to mechanically and chemically facilitate removal of a portion of a film deposed on the wafer""s surface. The pad may contain embedded abrasive materials to facilitate polishing. During CMP, a defect may appear on the wafer surface. Of course, any defect on the wafer surface has the potential of detrimentally affecting the performance of one or more chips. Additionally, the shrinking of semiconductor devices to smaller and smaller dimensions has significantly increased the sensitivity of devices to particle contamination. That is, smaller and smaller particles are now more likely to adversely affect the integrity of the device.
There is market pressure to continually reduce the costs of individual chips. Consequently, manufacturers strive to maximize their chip yield by reducing the number of defects per wafer, for example. Not only is it important to detect defects when they occur so that the wafer process may be adjusted, but it is also important to prevent defects before they occur. Accordingly, manufacturers attempt to detect the causes of defects so that the defects may be prevented.
The most likely cause of a defect is one or more xe2x80x9ckiller particles.xe2x80x9d For example, killer particles generally have a large enough size to cause a physical defect (e.g., a micro scratch, a short, or other damage) on the wafer during CMP. By way of example, one or more killer particle(s) may be rubbed against the wafer during CMP to form a scratch across the wafer surface.
Killer particles may originate from any number of sources. For example, killer particles may be present within the slurry itself. Thus, the slurry is usually inspected prior to the CMP process to detect killer particles therein. Unfortunately, killer particles may also be introduced into the slurry or onto the wafer as a result of contamination on the wafer, wafer carrier, or polishing pad. Additionally, portions of the wafer itself may break off to form killer particles.
Conventionally, if killer particles are introduced into the slurry and onto the wafer after the start of the CMP process, the killer particles are detected by removing the wafer from the CMP process to inspect off-line or ex-situ. That is, the wafer is transferred to an inspection tool. Since it is difficult and time-consuming to halt the CMP process and inspect the wafer, the wafer is only periodically inspected. As a result a killer particle may go undetected for a significant amount of time. Thus, killer particles may be detected after they have caused a defect on the wafer during the CMP process.
In summary, measurement apparatus and techniques for efficiently and reliably detecting anomalies, such as killer particles, in real time during CMP (i.e., in-situ) are needed.
Accordingly, the present invention addresses the above problems by providing apparatus and methods for detecting anomalies during the CMP process. In general terms, a hole is provided in the platen and pad of the CMP system. In one embodiment, an optical element is placed within the hole to provide an optical path for measurement of the sample and/or detection of anomalies associated with the sample. A fluid may also be flowed between the optical element and sample to clear away debris from the optical path.
In one embodiment, the invention pertains to a system for detecting anomalies associated with a sample. The system includes an objective arranged proximate to a sample while the sample is undergoing chemical mechanical polishing and a beam source arranged to generate an incident beam and direct the incident beam through the objective and toward the sample while the sample is undergoing chemical mechanical polishing. The system also includes a sensor arranged to detect a scattered beam reflected from at least one anomaly associated with the sample while the sample is undergoing chemical mechanical polishing. The scattered beam is in response to the incident beam. The scattered beam indicates a characteristic of the anomaly. In a preferred embodiment, the characteristic is particle size.
In another embodiment, an in-situ chemical-mechanical polishing apparatus for polishing a sample with a polishing agent and monitoring the sample is disclosed. The apparatus has a polishing table having a viewing opening and a sample mount arranged to hold the sample over the polishing table. The polishing table and sample mount are arranged to receive a polishing agent between the sample and the polishing table and to polish the sample by moving the polishing table and the sample mount relative to each other. The apparatus also includes an optical element proximate the viewing opening. The optical element is configured to receive an optical signal and direct it through the viewing opening to the sample. The apparatus further includes a measurement device arranged to detect a scattered beam resulting from the optical signal and at least one anomaly associated with the sample.
In another embodiment, a chemical mechanical polishing pad having a hole is disclosed. The hole is configured to receive an optical element that directs a beam towards the sample and a substantially transparent fluid flowing between the optical clement and the sample such that at least a portion adjacent to the sample is substantially cleared of debris. The optical element and the fluid direct the beam towards the sample.
In another aspect, the invention is directed towards a method of detecting anomalies on a sample. During a chemical mechanical polishing procedure being performed on a sample, an incident beam is directed towards the sample. At least one non-specular beam resulting from the incident beam and at least one anomaly associated with the sample is collected. The non-specular beam is analyzed to determine whether the at least one anomaly is a killer particle. In a preferred embodiment, when it is determined that the at least one anomaly is a killer particle, the chemical mechanical polishing procedure is adjusted.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example the principles of the invention.